The invention relates to the use of a hot-melt adhesive having a high hardness for the adhesive bonding of metal films or foils, paper films or foils, and/or plastic films or foils, such that the adhesive can be applied in a thin layer. The invention further relates to a method for adhesively bonding a metal film or foil, paper film or foil, and/or plastic film or foil onto a substrate.
The adhesive bonding of films or foils using adhesives is known. It is known, for example, to adhesively bond films or foils onto a variety of workpieces for visual design, or as surface protection. The adhesives are selected in accordance with the different substrates. It is known in this context to utilize reactive adhesives. These result, after they have crosslinked, in good mutual adhesion among the substrates. A disadvantage of such systems, however, is that a certain time is required for final curing, which can have a disadvantageous effect on a subsequent post-processing operation.
It is also known to use aqueous adhesives on, for example, wood substrates. Any possible moisture can be absorbed by the substrate, which can result in an acceleration of the adhesive operation. This property is also disadvantageous, however, since changes in shape and surface cannot be ruled out.
EP 2191947 A1 is also known. This describes a method and an apparatus for coating solid workpieces, the latter being adhesively bonded to a flexible coating material. A thermoplastic adhesive can be applied in this context together with the coating material; it is also possible, however, for a pre-coated film or foil to be bonded. Bonding occurs as a result of pressure and heating.
WO 2001/062492 A2 is furthermore known. It describes a wood substrate that is adhesively bonded to a decorative layer. Hot-melt adhesives having a high Shore D hardness, which encompass in particular polystyrene-based polymers, are disclosed for bonding.
The aforesaid adhesives for bonding flexible films or foils to planar substrates produce a variety of utilization problems. Reactive adhesives require a longer reaction time in order to build up final adhesion. Physically curing adhesives based on solutions or aqueous systems result in processing problems due to the fact that the solvent can damage the substrate surface, or that hazards in the working environment are a concern with organic solvents.
Known hot-melt adhesives usually have insufficient hardness to generate a solid surface. If the glass transition temperature of the binding agents is increased or if fillers are added, the application temperature then rises. For film or foil bonding, however, it is necessary for an elastic, non-brittle bond to be obtained; in addition, substrates must not be damaged in the course of application. If the adhesive layer is too brittle or is applied too thickly, damage occurs in the composite bond and the heat that is introduced can cause deformation of the substrates.